Mark the object where you want to insert the power rail.
Depending on the needed power rail type select either 'Objects > Power rail left' or 'Objects > Power rail right'.
The 'Power rail left/right' menu items are inactive if the corresponding power rail type cannot be connected to the selected object (e.g., directly to a formal parameter or a left power rail to a coil output).
It is not possible to insert a power rail which is not connected to any object.